The present invention involves an improved sputtering system, computer controlled to compensate for both long term and short term deviations from desired performance.
In the deposition of thin films, control of parameters such as film thickness, uniformity and the like are of critical importance. For most coating applications, and particularly in a production context, sputtering techniques have proven to be advantageous in achieving desired specifications for a wide variety of materials. It is known, however, that certain components of sputter coating apparatus are subject to deterioration; for example, the target (cathode), which is the source of sputterant, erodes under ion bombardment in such fashion as to significantly alter the geometry of the cathode surfaces during the useful life thereof. U.S. patent application No. 805,485, now U.S. Pat. No. 4,100,055, assigned to the assignee of the present invention, discloses an improved initial cathode shape which yields a longer useful life and thus greater integrated mass transfer of sputterant than achieved in the prior art. It has been pointed out in the above-referenced application that the power dissipated in the plasma, as well as the cathode geometry, is subject to a dependence on cumulative usage of the particular cathode. It is apparent that the rate of deposition reflects a similar variation. In the prior art, an independent deposition rate monitor provided, a deposition rate signal for use in a feedback loop to control the excitation source of the plasma discharge.